Vertically movable elevator car gates and landing doors are commonly used in freight elevator systems. For reasons of economy it is desirable to employ a single master door operator for operating the car gates and the doors at each landing. The vertically movable car gates are usually of the bypassing two-speed type although biparting type gates are also sometimes used. With either type of gate, however, the upper gate may be driven up or down to in turn cause the other gate to be driven up or down through a chain and sprocket system. The present invention finds use with either the biparting or the bypassing vertically movable gates.
As an elevator car approaches a landing it is desirable that the gate and landing door begin to open before the car comes to a complete stop. This is known in the art as advance door opening and is an advantageous feature of any elevator system because of the savings in time. It is also desirable that the gates and landing doors open and close in mutual synchronism. Both of these features are provided by the present invention. Moreover, the speed at which the gates and doors are opened and closed by the master door operator of the present invention follows one-hundred eighty degrees of a sine wave whereby the gates and doors move slowly away from and slowly into the fully open and closed positions.